The New Sudoku Players' Forum

[AnotherLife]

Hello everyone!
I am back to the forum and I start to post some new puzzles for you. This sudoku is formally rated below extreme, but will anybody try to solve it without computer assistance?

Code: Select all

|.9.|..2|4.5|
|..4|...|...|
|5.2|.9.|..8|
|---+---+---|
|...|3.9|.86|
|...|.2.|...|
|42.|8.6|...|
|---+---+---|
|7..|.6.|9.4|
|...|...|7..|
|2.9|7..|.5.|

.9...24.5..4......5.2.9...8...3.9.86....2....42.8.6...7...6.9.4......7..2.97...5.

[eleven]

Code: Select all

 *------------------------------------------------------------------*
 | e368   9     178   |  16   f1378    2       |  4    e137   5     |
 |  368   137   4     |  156   13578   13578   |  13    2     9     |
 |  5     137   2     |  4     9       137     |  6     137   8     |
 |--------------------+------------------------+--------------------|
 |  1     57    57    |  3     4       9       |  2     8     6     |
 |  9     8     6     |  15    2       157     |  135   4     137   |
 |  4     2     3     |  8     157     6       |  15    9     17    |
 |--------------------+------------------------+--------------------|
 |  7    c135   158   |  2     6       1358    |  9    b13    4     |
 | d38    4     158   |  9     1358    1358    |  7     6     2     |
 |  2     6     9     |  7     1-3     4       |  8     5    a13    |
 *------------------------------------------------------------------*

3r9c9 OR 3r7c8 forcing 3r8c1, therefore 3r1c5 => -3r9c5

Code: Select all

 *-------------------------------------------------*
 |  6    9   #78   |  1 #38    2     |  4  37   5  |
 |  38   37   4    |  6  58    57-8  |  1  2    9  |
 |  5    1    2    |  4  9     7-3   |  6  37   8  |
 |-----------------+-----------------+-------------|
 |  1    57   57   |  3  4     9     |  2  8    6  |
 |  9    8    6    |  5  2     1     |  3  4    7  |
 |  4    2    3    |  8  7     6     |  5  9    1  |
 |-----------------+-----------------+-------------|
 |  7    35  #58   |  2  6    #38    |  9  1    4  |
 |  38   4    1    |  9  5-38  358   |  7  6    2  |
 |  2    6    9    |  7  1     4     |  8  5    3  |
 *-------------------------------------------------*

Skyscraper and w-wing 83 in r17 => -38r23c6,r9c5; stte

[Cenoman]

Code: Select all

 +--------------------+------------------------+--------------------+
 | a368*  9     178   |  16   a1378*   2       |  4    b137*  5     |
 |  368   137   4     |  156   13578   13578   |  13    2     9     |
 |  5     137   2     |  4     9       137     |  6     137   8     |
 +--------------------+------------------------+--------------------+
 |  1     57    57    |  3     4       9       |  2     8     6     |
 |  9     8     6     |  15    2       157     |  135   4     137   |
 |  4     2     3     |  8     157     6       |  15    9     17    |
 +--------------------+------------------------+--------------------+
 |  7     135   158   |  2     6       1358    |  9    c13*   4     |
 | a38*   4     158   |  9    a1358*  a1358#   |  7     6     2     |
 |  2     6     9     |  7     1-3     4       |  8     5    d13*   |
 +--------------------+------------------------+--------------------+

1. Almost Finned X-Wing: [FXW(3)r8c56 = r8c1 - r1c1 = r1c5] = (3)r1c8 - r7c8 = r9c9 => -3 r9c5; 16 placements & locked sets

Code: Select all

 +-----------------+-------------------+-----------------+
 |  6    9    78   |  1    38    2     |  4    37   5    |
 |  38   37   4    |  6    58    57+8  |  1    2    9    |
 |  5    1    2    |  4    9     37    |  6    37   8    |
 +-----------------+-------------------+-----------------+
 |  1    57   57   |  3    4     9     |  2    8    6    |
 |  9    8    6    |  5    2     1     |  3    4    7    |
 |  4    2    3    |  8    7     6     |  5    9    1    |
 +-----------------+-------------------+-----------------+
 |  7    35   58   |  2    6     38    |  9    1    4    |
 |  38   4    1    |  9    5+8-3 58+3  |  7    6    2    |
 |  2    6    9    |  7    1     4     |  8    5    3    |
 +-----------------+-------------------+-----------------+

2. BUG+3: (8r8c5|3r8c6) == (8)r2c6 - (8=3)r1c5 => -3 r8c5; ste

[marek stefanik]

Similar to eleven's:

Code: Select all

.---------------.-------------------.---------------.
|#368  9    178 | 16  #1378   2     | 4   #137  5   |
| 368  137  4   | 156  13578  13578 | 13   2    9   |
| 5    137  2   | 4    9      137   | 6    137  8   |
:---------------+-------------------+---------------:
| 1    57   57  | 3    4      9     | 2    8    6   |
| 9    8    6   | 15   2      157   | 135  4    137 |
| 4    2    3   | 8    157    6     | 15   9    17  |
:---------------+-------------------+---------------:
| 7   #135  158 | 2    6      1358  | 9    1–3  4   |
|#38   4    158 | 9    1358   1358  | 7    6    2   |
| 2    6    9   | 7   #13     4     | 8    5   #13  |
'---------------'-------------------'---------------'

3r19b7\c158r7b9 => –3r7c8

Code: Select all

.------------.-------------.----------.
| 6   9  #78 | 1 #38   2   | 4  37  5 |
|#38  37  4  | 6  58   57–8| 1  2   9 |
| 5   1   2  | 4  9    37  | 6  37  8 |
:------------+-------------+----------:
| 1   57  57 | 3  4    9   | 2  8   6 |
| 9   8   6  | 5  2    1   | 3  4   7 |
| 4   2   3  | 8  7    6   | 5  9   1 |
:------------+-------------+----------:
| 7   35  58 | 2  6    38  | 9  1   4 |
|#38  4   1  | 9  35–8 58+3| 7  6   2 |
| 2   6   9  | 7  1    4   | 8  5   3 |
'------------'-------------'----------'

8r1c1\r8c5b2 => –8r8c5, 8b8\c6 => –8r2c6, BUG+1 => r8c6=3, stte

[AnotherLife]

Thanks for your solutions!
This is an example of a puzzle unsolvable via AICs with ALS's, and I wonder why it is rated below extreme. I think that the current rating system does not reflect the actual complexity of sudokus for manual solving.

Eleven's solution is based on forcing chains.
Cenoman used a kraken fish, and I like this approach most because he started from an incomplete structure (almost finned x-wing) and made further conclusions via chains.
Marek's solution reminds me of the Frankenstein Swordfish found by the programs: 3r19b7\c158 fr7c2,r9c9 => r7c8<>3.
All three solutions use advanced methods, and it's great if you have found them by yourselves.

I called this puzzle 'Strange Creature' because its solution should be based on a kraken fish or a Frankenstein fish, really strange kind of fish.

[eleven]

In my eyes the puzzle is overrated. It was solvable straightforward.
If you have solved newspaper puzzles you know, that some quads are easier to spot than some naked triples. So what ? It probably would need an AI rating to reflect that.
If you want (patience) challenging puzzles for manual solvers, have a look at the ER 7+ puzzles in the 'Patterns Game' thread. Those are the ones no one likes to do manually (at least until it is solved).

[denis_berthier]

.

Code: Select all

Resolution state after Singles and whips[1]:
   +-------------------+-------------------+-------------------+
   ! 368   9     178   ! 16    1378  2     ! 4     137   5     !
   ! 368   137   4     ! 156   13578 13578 ! 13    2     9     !
   ! 5     137   2     ! 4     9     137   ! 6     137   8     !
   +-------------------+-------------------+-------------------+
   ! 1     57    57    ! 3     4     9     ! 2     8     6     !
   ! 9     8     6     ! 15    2     157   ! 135   4     137   !
   ! 4     2     3     ! 8     157   6     ! 15    9     17    !
   +-------------------+-------------------+-------------------+
   ! 7     135   158   ! 2     6     1358  ! 9     13    4     !
   ! 38    4     158   ! 9     1358  1358  ! 7     6     2     !
   ! 2     6     9     ! 7     13    4     ! 8     5     13    !
   +-------------------+-------------------+-------------------+
96 candidates.

Without artificial restrictions on the number of steps, the puzzle is an easy one, solvable in Z3 (using only reversible chains):

Code: Select all

finned-x-wing-in-rows: n1{r9 r6}{c5 c9} ==> r5c9≠1
z-chain[3]: b7n3{r7c2 r8c1} - r1n3{c1 c5} - r9n3{c5 .} ==> r7c8≠3
singles ==> r7c8=1, r9c9=3, r5c9=7, r6c9=1, r6c7=5, r5c7=3, r2c7=1, r6c5=7, r9c5=1, r8c3=1, r3c2=1, r1c4=1, r5c4=5, r2c4=6, r5c6=1, r1c1=6
whip[1]: b1n3{r2c2 .} ==> r2c5≠3, r2c6≠3
whip[1]: r8n5{c6 .} ==> r7c6≠5
finned-x-wing-in-columns: n8{c1 c6}{r2 r8} ==> r8c5≠8
whip[1]: b8n8{r8c6 .} ==> r2c6≠8
biv-chain[3]: b2n3{r1c5 r3c6} - r7c6{n3 n8} - c3n8{r7 r1} ==> r1c5≠8
stte

[AnotherLife]

In my eyes the puzzle is overrated. It was solvable straightforward.

Hello, eleven,
I have not tried to solve this puzzle by myself but I have generated it so that it should not be solved via AICs with ALS's and basic fishes. Do you agree that forcing chains are methods of last resort? Well, I use to think so because I have learned the theory from HoDoKu website. Such methods are coloured red in both HoDoKu and YZF_Solver, and these programs use a Sashimi Franken Swordfish in their default solutions of this puzzle, which is very hard to find, in my opinion. Maybe it is my drawback that I do not use such methods in manual solving, and AICs with ALS's are more understandable for me.

If you do not want me to post puzzles on this forum, please, tell me. I have my own way in sudoku.

Regards, Bogdan

[eleven]

Hi Bogdan,

in this case my first elimination was easier to find for me than a longer bivalue chain is. Of course normally AIC's are easier to spot than 3-way-deductions or Krakens (which it was). But here i just had to follow obvious links for digit 3.

Of course i want you to continue posting puzzles - and thanks for that one.